ISO 6721-8:2019

INTERNATIONAL ISO
STANDARD 6721-8
Second edition
2019-04
Plastics — Determination of dynamic
mechanical properties —
Part 8:
Longitudinal and shear vibration —
Wave-propagation method
Plastiques — Détermination des propriétés mécaniques
dynamiques —
Partie 8: Vibrations longitudinale et en cisaillement — Méthode de
propagation des ondes
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Testing device . 2
5.1 Apparatus . 2
5.1.1 Method A: Immersion method . 3
5.1.2 Method B: Transducer contact method . 3
5.2 Transducers . 3
5.3 Transit-time measurement equipment . 3
5.4 Temperature measurement and control . 4
6 Test specimens. 4
6.1 General . 4
6.2 Shape and dimensions . 4
6.3 Preparation . 4
7 Number of specimens . 4
8 Conditioning . 4
9 Procedure. 4
9.1 Test atmosphere . 4
9.2 Measuring the specimen dimension. 5
9.3 Performing the test. 5
9.3.1 Method A: Immersion method . 5
9.3.2 Method B: Transducer contact method . 5
9.3.3 Measurement of the specimen density . 5
9.4 Varying the temperature . 6
10 Expression of the results . 6
10.1 Symbols . 6
10.2 Determination of the longitudinal wave velocity v  . 6
L
10.2.1 Method A: Immersion method . 6
10.2.2 Method B: Transducer contact method . 7
10.3 Determination of the transverse wave velocity v . 7
T
10.3.1 Method A: Immersion method . 7
10.3.2 Method B: Transducer contact method . 8
10.4 Calculation of dynamic properties . 8
10.5 Influence of material anisotropy . 8
11 Precision . 9
12 Test report . 9
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
This second edition cancels and replaces the first edition (ISO 6721-8:1997), which has been technically
revised. The main changes compared to the previous edition are as follows:
— the document has been revised editorially;
— normative references have been changed to undated.
A list of all parts in the ISO 6721 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 6721-8:2019(E)
Plastics — Determination of dynamic mechanical
properties —
Part 8:
Longitudinal and shear vibration — Wave-propagation
method
1 Scope
This document describes an ultrasonic wave propagation method for determining the storage
components of the longitudinal complex modulus L* and the shear complex modulus G* of polymers
at discrete frequencies typically in the range 0,5 MHz to 5 MHz. The method is suitable for measuring
materials with storage moduli in the range 0,01 GPa to 200 GPa and with loss factors below 0,1 at
around 1 MHz. With materials that have a higher loss, significant errors in velocity measurement are
introduced through waveform distortion and can only be reduced using procedures that are outside
the scope of this document.
The method allows measurements to be made on small specimens, typically 50 mm × 20 mm × 5 mm,
or small regions of larger specimens or sheets. It is therefore possible to obtain information on the
homogeneity or anisotropy (see 10.5) of modulus in a specimen.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 1183-1, Plastics — Methods for determining the density of non-cellular plastics — Part 1: Immersion
method, liquid pyknometer method and titration method
ISO 1183-2, Plastics — Methods for determining the density of non-cellular plastics — Part 2: Density
gradient column method
ISO 1183-3, Plastics — Methods for determining the density of non-cellular plastics — Part 3: Gas
pyknometer method
ISO 6721-1, Plastics — Determination of dynamic mechanical properties — Part 1: General principles
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6721-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
longitudinal modulus
ratio of an uniaxial tensile or compressive stress applied to a specimen to the resulting uniaxial strain
when the strain in a plane transverse to the axis of applied stress is zero
Note 1 to entry: See ISO 6721-1 for relationships between this and other moduli.
3.2
longitudinal acoustic wave
sound wave in which the particle displacement is in the direction of wave propagation
3.3
transverse acoustic wave
sound wave in which the particle displacement is perpendicular to the direction of wave propagation
3.4
bulk wave
mode of propagation of an acoustic wave in a material whose boundaries normal to the direction of
propagation are infinitely remote
Note 1 to entry: This mode is realized in practice for waves whose wavelength is much less than the dimensions
of the specimen transverse to the direction of propagation.
Note 2 to entry: In practice, the acoustic wave frequency is then ultrasonic.
4 Principle
Measurements are made of the velocity of longitudinal and transverse acoustic waves in a specimen
and the specimen density. The frequency of the wave is chosen so that its wavelength in the specimen
is significantly less than the specimen dimensions in a plane transverse to the direction of wave
propagation. The wave then propagates as a
...